WOAD (Isatis tinctoria)
Woad has been used for thousands of years to dye wool and other natural fibres. It is native to Northern Europe and the British Isles. It is closely related to broccoli and cabbage.
Both indigo and woad provide us with a beautiful blue dye. The chemical which gives the blue dye is called indigotin. The indigo plants yields 10 times more indigotin than woad and are therefore much stronger. However it is not generally possible to grow indigo in the British Isles as it requires a hot and humid climate and a long growing period. Although I did once experiment with 100 indigo plants in a forty foot long polytunnel with some measure of success.
Dyeing with woad is more complicated than with other natural dyes – you could say it is in a class of its own!
Woad is a biennial. It grows its leaves in the first year in small compact clusters about eight inches in height. It is the leaves that contain the blue dye. In the second year it grows up to five foot in height and in about May produces a beautiful display of bright yellow flowers.
The flowers do not yield any dye pigments and after a few weeks they give a multitude of black wing like seeds before the plant dies.
When the seeds are ready, collect, dry and store some for next years crop, however they self seed readily and care must be taken as they can become invasive. Seeds sown during October will be ready for picking the following June. Seeds sown in March will be ready later in the summer. The woad seeds can be sown anytime throughout the warm season and germination is rapid. An early crop from seeds that have been sown the previous autumn can be harvested four or five times throughout the summer and autumn of the following year. However the optimum depth of colour is achieved from July – September pickings.
The benefits of woad are to offer an alternative to the harmful chemicals used in synthetic indigo dyeing.
Dying with Woad
There are several ways of dyeing with woad.
- You can dye with freshly picked leaves.
- You can extract the dye to store as a powder.
- You can make a fermentation vat.
- You can store it as a liquid.
- You can use the exhausted leaves to make a pink dye.
Woad benefits from alkaline soil. Before planting apply garden lime and try to attain a pH of between 7 and 8. Woad benefits from a nitrogen rich soil. I grow huge amounts of comfrey plants (Bocking 14) which make a marvelous organic fertilizer packed with nitrogen (Bocking 14 also has numerous medicinal benefits). After each picking, I top feed with comfrey tea to increase production and depth of colour.
Move your woad crop each year if possible because it is a heavy feeder and depletes the land it grows on of nutrients, which is reflected in the depth of colour when extracted.
Woad chemical vat
- 20 grams of woad pigment
- 16 grams of soda ash
- 20 grams spectralite (thiourea dioxide)
- 8 litres soft water (rain water)
- Maximum 400 grams of yarn, fibre or silk to be dyed
You will also need;
- 10 litre stainless steel bucket with lid
- 2 x 1 litre plastic jars with screw lids
- Digital scales
- pH paper
- 2 stir sticks
- Strong rubber gloves
The pH should read between 9 and 10 – no higher.
This solution should dye 400g of fibre.
To avoid disappointment ensure the spectralite is fairly fresh as it only has a shelf life of about 1 year,
It is very important that your fibre is perfectly scoured and clean before attempting to dye otherwise you may find you have disappointing results, with uneven colour.
Woad does not require a mordant before or during the dye process.
Soak the fibre overnight to open up the fibres enabling the dye to penetrate more evenly and prevent the fibre from floating.
Make the woad stock solution as follows:
In the first jar carefully weigh 16 grams soda ash. Stir in 500ml of hot rain water and stir thoroughly using the stirring rod, ensuring that the rod is long enough to reach the bottom of the jar, until the powder is dissolved.
In the second jar weigh 20 grams of woad pigment. Add 50ml of warm rain water – no more than 50 degrees centigrade and mix to a smooth paste. Carefully add this paste to the soda ash solution, and stir gently.
Replace the lid and allow to stand for 1 hour – until the liquid clears. Stand the jar in a bowl of tepid/warm water and try to maintain a constant heat of about blood temperature. (41 degrees C or 108 F)
Meanwhile slowly heat 10 litres of rain water to 50 degrees centigrade or 120 degrees Fahrenheit (no hotter) in the stainless steel bucket. When the water has reached the required temperature very carefully add the woad solution to the bucket of rainwater. Sprinkle 20 grams of spectralite into the bucket. It is most important that you do not introduce any air bubbles into the solution from now on. Stir very carefully. Replace the lid and allow to stand for 2 hours, maintaining a constant temperature of 50 degrees centigrade.
Check the pH which should read between 9 and 10.
When the vat is ready it should have a yellow-green liquid beneath a bronze blue bloom.
Now the big moment has arrived! Wearing rubber gloves squeeze the fibre which has been soaking for several hours and when there are no drips remaining carefully submerge the yarn, fibre or material into the dye vat. Squeezing the fibre assists in preventing any unwanted air entering the vat.
Gently “work” the yarn or fibre under the surface of the solution by carefully squeezing the liquid through the fiber for a minute or two, without creating any air bubbles. Leave the fibre in the covered vat for 10 minutes, then remove it very carefully either by gently sliding it over the side of the bucket into a bowl or by going under the surface of the liquid with your gloved hands and very carefully and gently gathering the yarn together and squeezing the liquid out of the yarn whilst still under the surface of the liquid and grasping it in your hands, lift it out of the bucket without making any drips. I prefer this method as I don’t waste any of the precious dye which tends to happen when I slide it out.
Shake and hang the yarn or fibre to oxidise. It is fascinating to watch the change of colour from yellow-green to blue. The general rule is to hang the dyed fibre for the same length of time it was submerged in the vat – in this case 10 minutes.
It is preferable to keep immersing and oxidising the fibre until the required colour is obtained, rather than keeping it submerged for a long period of time. However, the second and subsequent dips should be short, about 1 or 2 minutes each time, followed by an airing of 10 – 15 minutes then rinsing before each subsequent dip. – This gradually builds up the depth of colour. The more often you immerse and oxidise the yarn, the darker the blue. However there will come a point where the fibre reaches the maximum depth of blue that the vat will yield and in fact it would be a mistake to attempt to make it any darker as this stage by prolonged immersion, as the spectralite will begin to strip the fibre of the pigment and the reverse will happen – the fibre will become paler.
Leave the fibre to air for 48 hours or longer.
Finally, wash the yarn in hand hot water adding 2 tablespoons of white vinegar to the final rinse and leave for fifteen minutes to prevent any possible bleeding of the colour.
The solution will keep for about 4 weeks if kept covered in a warm place. If the solution turns blue it means that there is free oxygen in it, so just add a little more spectralite – one teaspoon at a time. Let the solution rest for 30 minutes after each addition of spectralite.
This woad vat will dye approximately 1.5 kg of yarn before it becomes exhausted.
If you require several ounces or grams of yarn or fibre for a project it is advisable to have the entire amount of yarn ready to dye at the same time, as dyeing at a later date will not produce the exact shade on another occasion.
Although many other plants yield a variety of natural dyes which are initially very pretty, the above dye plants have the best reputation for light and wash fastness and give the primary colours required for over dyeing which can extend the range enormously. If you have limited space to “grow your own” you can’t go wrong with the above selection. However bear in mind the madder root will take 3 – 5 years to develop before it can be harvested – but is well worth the wait!
It is important to wash dyed materials with a soap which has a neutral pH otherwise you may find the colour shifts giving you an unwanted colour change. Check the pH on your detergent to be on the safe side.
I grow and use soapwort which is an ancient herb native to Europe. It is traditionally a cleansing herb, used for hundreds of years for cleaning unprocessed wool and fabrics as well as a people cleanser. It is pH neutral. It is a gentle effective cleaner, used especially on delicate fabrics that can be harmed by modern synthetic soaps. It has been used to clean the Bayeaux tapestry. It effects a lustre in the fabric and is a very safe soap to use after the dyeing process is complete.